Cleaning agent for food-industry facilities, its use and method of cleaning such facilities using the agent

ABSTRACT

An aqueous alkaline composition for cleaning equipment used in the food industry wherein the composition contains potassium hydroxide or a mixture of potassium hydroxide and sodium hydroxide and wherein the potassium hydroxide is present in an amount of at least 20% by weight, based on the weight of hydroxide present in the composition. A process for regenerating the cleaning solution is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a water-containing alkaline cleaningformulation containing potash lye for equipment used in the foodindustry.

The invention also relates to a process for cleaning equipment used inthe food industry with an alkaline cleaning formulation which isregenerated by membrane filtration, the permeate being recycled.

It is known that equipment used in the food-processing industry, forexample tanks, pipelines, bottling plants and the like, can be cleanedwith alkaline cleaning solutions. These cleaning solutions or liquorsessentially consist of a 2% soda lye containing added cleaningenhancers, for example defoamers and emulsifiers. In principle, potashlye could be used instead of soda lye because it produces the samecleaning result. However, soda lye is used for reasons of cost. Onlywhere low outside temperatures prevail is potash lye added in smallquantities to the soda lye in order to lower the crystallization pointof the cleaning concentrate. However, the potash lye always makes upconsiderably less than 20% by weight of the hydroxide total.

The alkaline cleaning solutions often contain an addition ofethylenediamine tetraacetic acid (EDTA) in the form of its disodium saltbecause EDTA—as the only complexing agent in aqueous alkaline cleaningsolutions—is capable of dissolving mineral soils, such as calcium andmagnesium salts, for example in the form of limescale, milk scale, beerscale and the like.

In recent years, an integrated cleaning and disinfecting technique knownas cleaning in place (CIP) has been successfully applied. Thecorresponding fully automatic cleaning systems clean all storage tanksand pipelines automatically after each production cycle. The cleaningformulation and cleaning process according to the invention areparticularly suitable for use in the CIP process.

2. Discussion of Related Art

It is known that wastewater pollution by spent cleaning solutions can bereduced and the economy of the cleaning process improved by regeneratingthe spent cleaning solution in membrane filtration units. To this end,part of the cleaning solution is transferred from a collecting tank to abuffer tank and pump-circulated from there through a membrane system inwhich it undergoes crossflow filtration. One such regenerating processis known from WO 95/27681 A1. The permeate consisting of water and sodalye is returned to the collecting tank for the cleaning solution. Theorganic soils collect in the buffer tank of the membrane filtration unitand are periodically removed for disposal as waste. Since, in caseswhere EDTA-containing cleaning solutions are used, any introduction ofEDTA into the wastewater should be avoided on account of the poorbiodegradability of this compound and its ability to remobilize heavymetals in the environment, Israeli patent application IL 109 249proposes recovering the EDTA from the concentrates collecting in thebuffer tank by acidic precipitation. However, the addition of EDTA tothe cleaning solutions affects the performance of the nanofiltrationunit which is reflected in distinctly reduced flow. In addition, in thecase of cleaning equipment for the dairy industry and in the case ofEDTA-free cleaning solutions, it is known that the concentrate can befreed from the alkaline constituents by diafiltration and subsequentlyused as an animal feed or animal feed supplement. Diafiltration isnecessary to reduce the sodium content of the concentrate which is toohigh for its use as an animal feed. Unfortunately, the large volume ofwastewater accumulating in the diafiltration process and the high costof diafiltration are disadvantages.

The problem addressed by the present invention was to provide analkaline cleaning formulation and a process for cleaning equipment usedin the food industry of the type mentioned at the beginning which wouldenable cleaning to be carried out far more economically than in theprior art.

DESCRIPTION OF THE INVENTION

In the case of the water-containing alkaline cleaning formulation, thesolution to this problem as provided by the invention is characterizedin that the cleaning formulation contains only potash lye or a mixtureof potash lye and another alkali, more particularly soda lye, containingat least 20% by weight of potash lye, expressed as hydroxide and basedon the total amount of hydroxide present in the cleaning formulation, asits hydroxide component.

In the case of the cleaning process according to the invention, thesolution to the problem stated above as provided by the invention ischaracterized in that it is carried out with a cleaning solution ofwhich the hydroxide component consists solely of potash lye or of amixture of potash lye and another alkali, more particularly soda lye,containing at least 20% by weight of potash lye, expressed as hydroxideand based on the total amount of hydroxide present in the cleaningsolution.

It has surprisingly been found that the partial or complete replacementof sodium hydroxide by potassium hydroxide increases the performance ofthe membrane unit by at least 10 to 50%. Performance in this case isbased on the permeate flows achieved. Investment costs and the energyconsumption of the membrane filtration unit can thus be reduced. Higherconcentrations of the soil load removed are possible so that the volumeof the soil load is reduced and the yield of regenerated solution isincreased.

Another advantage was discovered. In contrast to the prior art where theconcentrate obtained is a mass which is fairly solid at room temperatureand which leads to problems during discharge from the buffer tank andduring subsequent processing, the concentrate obtained where thecleaning formulation according to the invention is used and in thepractical application of the process according to the invention is amass containing the soils which is liquid at room temperature and evenat a temperature of 0° C. On the one hand, this simplifies the wastelogistics; on the other hand, greater concentration can be achieved,providing for a higher nutrient content where the concentrate is used asan animal feed and for a higher energy content where it is used as afuel.

The advantages mentioned above were achieved with a minimum of only 20%by weight of potash lye, expressed as hydroxide and based on the totalamount of hydroxide present in the cleaning formulation. Thedisadvantage of the higher cost of using potash lye instead of soda lyeis negligible because the potash lye is largely regenerated.

In the nanofiltration of EDTA-containing cleaning solutions, theperformance of the membrane filtration unit is likewise increased byreplacement of the sodium salts by potassium salts. Disadvantagesarising during filtration through the use of EDTA can thus becompensated or even overcompensated simply by using potash lye and EDTAin the form of the free acid or its potassium salt. The disodium salt ofEDTA may also be used providing this does not increase the sodium ioncontent of the formulation beyond certain limits. If all alkali metalions are counted as alkali metal hydroxide, the potash lye content ofthe cleaning formulation, based on the total amount of hydroxide presenttherein, should not fall below 20% by weight. Generally speaking, theperformance of the filtration unit increases with the ratio of potassiumto sodium ions in the cleaning formulation, i.e. sodium-free cleaningsolutions produce the highest throughflow rates in l/m²h.

The cleaning formulation preferably contains a mixture of potash lye andanother alkali, preferably soda lye, containing at least 50% by weightof potash lye, expressed as hydroxide and based on the total amount ofhydroxide present in the cleaning formulation.

The advantage of the EDTA-free cleaning formulation containing at least50% by weight of potash lye lies in the possibility of directly usingthe soils filtered off without any aftertreatment as an animal feed, forexample as a pig feed, because a high potassium salt content can betolerated more readily than a high sodium salt content.

In one particularly preferred embodiment, the EDTA-free cleaningformulation contains potash lye alone as its hydroxide component. Byvirtue of its high content of potassium ions, the membrane filtrationconcentrate obtained in this case is a valuable animal feed supplement,particularly for pig feed.

Where the soils removed are to be used as an animal feed, it is also ofadvantage for the cleaning formulation to contain additives which areall suitable as animal feed supplements. Special physiologically safecleaning enhancers of the type in question, which are not used in knowncleaning formulations, include in particular phosphates, gluconatesand/or approved food-quality defoamers and emulsifiers.

In another advantageous embodiment, the cleaning formulation containsadditives present in the form of potassium salts in addition to thehydroxide components. On the one hand, the performance of the membranefiltration unit can be additionally increased in this case. A permeateflow of, for example, 50 l/m²h in the case of a conventional cleaningformulation based on soda lye can be increased to 70 l/m²h by replacingthe soda lye with potash lye. If the cleaning formulation additionallycontains potassium tripolyphosphate to enhance cleaning, the permeateflow additionally rises to 74 l/m²h.

Another advantage of these additives present in the form of potassiumsalts is their particular suitability as an animal feed supplement.

As mentioned above, the cleaning formulation according to the inventionmay be used with advantage for food-processing equipment having aregeneration unit for spent cleaning solutions. The cleaning formulationis particularly preferred for cleaning dairy equipment because theconcentrate obtained may be used without any further aftertreatment asan animal feed. There is generally no need for diafiltration or otheradditional working-up. Not only is there no need for expensivewaste-disposal of the soils separated off, these “soils” actuallyconstitute a new useful material. If, however, the high salt content isto be reduced by diafiltration, the filtration process may be carriedout much more quickly and hence economically in the case of the cleaningformulation and cleaning process according to the invention.

The concentrates obtained in the nanofiltration of EDTA-containingcleaning solutions can be subjected to step-by-step acidification torecover the EDTA. If the concentrate is nonspecifically acidified (asdescribed in Israeli patent application IL 109 249), almost all the dirtpresent in the concentrate is precipitated besides the EDTA. When theprecipitated EDTA filtered off is redissolved with a lye, the dirt isalso redissolved. If the resulting solution is added to the solutioncleaned by nanofiltration, the degree of soiling prevailing beforenanofiltration is virtually reestablished. By acidification in steps(fractional precipitation), most of the dirt can be precipitated beforethe precipitation point for EDTA. The precipitated dirt can then beremoved by simple filtration. If the pH value of the filtered solutionis further reduced, EDTA precipitates with a far lower content ofresidual soil. The EDTA filtered off can be reconverted into a solubleform with alkali and added, for example, to the nanofiltration permeate.Since EDTA remains to a certain extent both in the precipitated sludgeand in the solution from which it was precipitated, 80 to 90% of theEDTA originally used can be recycled by this method. However, the dirtfiltered off can no longer be used as an animal feed on account of itsresidual EDTA content.

Alkali-resistant nanofiltration membranes with a D value of 100 to 2,000dalton are preferably used in the process according to the invention toregenerate the cleaning solution. Membranes such as these are permeableto molecules with a molecular weight up to the D value mentioned, butretain molecules with a higher molecular weight.

In one particular embodiment, the membrane filtration is carried out onthe crossflow principle with a transmembranal pressure difference of 8to 25 bar.

In another preferred embodiment of the process according to theinvention, a cleaning solution containing only additives suitable asanimal feed supplements besides the hydroxide components is used forcleaning dairy equipment and the membrane filtration concentrateobtained is used as an animal feed or animal feed supplement.

A concentrate with a particularly high potassium content is far moresuitable for use as an animal feed, for example as a pig feed, thanconcentrates with high sodium contents. In another embodiment,therefore, the hydroxide components of the cleaning solution consistsolely of potash lye.

The known cleaning process is described first in the following withreference to the accompanying drawing which is a simplified flow chartof a CIP cleaning system followed by a regeneration unit for thecleaning solution. The description of the known process is followed bysome Examples which demonstrate the superiority of the process andcleaning formulation according to the invention to the prior art.

DESCRIPTION OF THE DRAWING

From a collecting tank 1 for the cleaning solution with a volume of 5 to30 m³, the solution which contains about 2% by weight of soda lye in theprior art and 2% by weight of potash lye according to the invention andwhich is heated to 60-70° C. is fed to the equipment (tanks, pipelines,etc. denoted by the reference numeral 2 in FIG. 1) to be cleaned. Thecleaning solution is circulated.

The soils gradually collecting in the cleaning solution are removed inthe regenerating section shown on the right of FIG. 1. To this end, partof the cleaning solution is transferred to the buffer tank 4 through apipe 3. This part of the cleaning solution is circulated through amembrane module 6 by a pressure pump 5. The soils collecting andsettling in the buffer tank 4 are periodically removed through a pipe 7.The permeate issuing from the membrane module is returned to thecollecting tank 1 through the return pipe 8.

EXAMPLE 1 (COMPARISON EXAMPLE)

An artificially soiled solution corresponding to practical conditionswith a temperature of 60 to 65° C. was used. It had been passed througha single-tube module with a membrane area of 0.042 m² and an MPT 34nanofiltration membrane (a product of Membrane Products) for 75 to 120mins. at a throughput of 1000 l/h (entry pressure 18 bar, exit pressure14 bar). The permeate side of the membrane was at atmospheric pressure.

In the case of a cleaning solution containing only 2% soda lye, thepermeate flow was 50 l/h m².

Where a cleaning solution containing only 2% potash lye was used, thepermeate flow increased to 70 l/h m².

When 0.1% by weight of gluconic acid was added to the cleaning solutioncontaining the potash lye, a permeate flow of 65 l/h m² was observed.When 0.25% by weight of potassium tripolyphosphate was added to thecleaning solution containing potash lye, a permeate flow of 73 to 75 l/hm² was observed.

These results reflect the clear superiority of the cleaning formulationand cleaning process according to the invention over the prior artbecause far higher performances were achieved. An additional advantagelies in the low sodium content of the concentrate obtained so that theconcentrate may readily be used without further aftertreatment as ananimal feed. In particular, there is no need for expensive diafiltrationwhich is necessary in the known process in order to reduce the sodiumcontent to tolerable levels.

EXAMPLE 2

An artificially soiled solution corresponding to practical conditionswith a temperature of 60 to 65° C. and an EDTA content of 0.7% by weightwas used. It had been passed through a single-tube module with amembrane area of 0.042 m² and an MPT 34 nanofiltration membrane (aproduct of Membrane Products) for 180 mins. at a throughput of 1000 l/h(entry pressure 18 bar, exit pressure 14 bar). The permeate side of themembrane was at atmospheric pressure.

In the case of a cleaning solution containing only 2% soda lye, thepermeate flow was 50 l/h m².

When 0.7% by weight of EDTA was added to the cleaning solutioncontaining the soda lye, a permeate flow of only 30 l/h m² was observed.

Where a cleaning solution containing only 2% potash lye was used, thepermeate flow increased to 70 l/h m².

When 0.7% by weight of EDTA was added to the cleaning solutioncontaining the potash lye, a permeate flow of 60 l/h m² was observed,i.e. a 20% improvement over the EDTA-free cleaning solution containingsoda lye.

These results reflect the clear superiority of the cleaning formulationand cleaning process according to the invention over the prior artbecause far higher performances were achieved and were not as badlyaffected by the addition of EDTA as the known cleaning formulations andcleaning processes.

What is claimed is:
 1. The process of cleaning equipment used in thefood industry, comprising contacting said equipment with an aqueousalkaline composition containing potassium hydroxide or a mixture ofpotassium hydroxide and sodium hydroxide wherein said potassiumhydroxide is present in an amount of at least 20% by weight, based onthe weight of hydroxide present in said composition, regenerating saidaqueous alkaline composition by membrane filtration with ananofiltration membrane having a D value of 100 to 2,000 daltons to forma permeate, and recycling said permeate into the aqueous alkalinecomposition for contact with the food industry equipment.
 2. A processas in claim 1 wherein said potassium hydroxide is present in an amountof at least 50% by weight, based on the weight of hydroxide present insaid composition.
 3. A process as in claim 1 wherein said compositioncontains only potassium hydroxide as the hydroxide.
 4. A process as inclaim 1 where in composition further contains cleaning componentssuitable for use as animal feed supplements.
 5. A process as in claim 1wherein said composition further contains phosphates, gluconates andfood-quality defoamers and emulsifiers.
 6. A process as in claim 1wherein said composition further contains cleaning components in theform of potassium salts.
 7. A process as in claim 1 wherein saidcomposition further contains ethylenediamine tetraacetic acid or saltsthereof.
 8. A process as in claim 7 wherein said ethylenediaminetetraacetic acid is present as a potassium salt.
 9. A process as inclaim 7 wherein said ethylenediamine tetraacetic acid is present as thedisodium salt and said potassium hydroxide is present in an amount of atleast 20% by weight, based on the weight of hydroxide present in saidcomposition.
 10. A process as in claim 1 wherein said food industryequipment comprises dairy equipment.
 11. A process as in claim 1 whereinsaid membrane filtration is conducted by crossflow filtration at atransmembranal pressure difference of 8 to 25 bar.
 12. A process as inclaim 1 wherein the membrane filtration concentrate obtained is usefulas an animal feed or animal feed supplement.
 13. A process as in claim 1wherein ethylenediamine tetraacetic acid or salts thereof obtained fromsaid regenerating step is recovered by fractional precipitation,dissolved with alkali metal hydroxide, and returned to said aqueousalkaline composition.